Orlando police have released images and video of the frantic first few minutes of the Pulse nightclub massacre in June, as an off-duty officer tried to take down killer Omar Mateen as he carried out the deadliest mass shooting in American history.

Stills taken from bodycam video reveal Officer Adam Gruler using a pickup truck as cover and firing at Mateen who had already killed at least half of his 49 victims.

Revealed as part of a 78-page presentation given by Orlando Police Chief John Mina, the devastating report lays bare the carnage that unfolded in front of Officer Gruler as Mateen opened fire on the dancefloor at 2.02am on June 12.

The images include Gruler, who was working an off-duty job at Pulse that morning, firing shots at Mateen in the club's doorway.

Gruler called a signal 43, which means an officer needs help. When help arrived minutes later, Gruler told them, 'He's in the patio!' and shot multiple rounds toward Mateen.

The report also reveals that nearly half of the 49 victims in the mass shooting last June died on the dance floor without a chance to react or run for help.

Another 13 died in bathrooms while waiting for help during a three-hour hostage standoff.

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Adam Gruler, who was working an off-duty job at Pulse that morning, is seen firing shots at Mateen in the club's doorway

Officers tend to a person with a facial wound outside the club on June 12 in the image taken from bodycam

This officer photo shows the chaos outside the club after the fatal attack which killed 49

Another boy cam still shows officers gathered on the ground behind a truck

Body cam footage shows officers entering the club after the three-hour standoff

A new report from the Orlando police reveals that 13 of the 49 Pulse nightclub shooting victims died in the bathrooms while waiting for help during the three-hour standoff between the gunman and cops

The south bathroom in the Pulse Nightclub, where Omar Mateen killed 49 people, in Orlando, Florida, U.S. is pictured in this image released as part of a briefing document by the Orlando Police on April 13, 2017

After three hours, officers knocked out the walls to both bathrooms to let survivors escape

Gunman Omar Mateen (pictured) was shot dead by police around 5:02am, when cops finally breached the club

Surveillance video from inside the clubs captures also shows Mateen running from the main dance floor toward the bathrooms.

Nine people died in the north bathroom, where Mateen, 29, was barricaded for much of the standoff, according to the report. Four died in the south bathroom. Eleven died at the hospital or in triage areas set up outside the club.

At 5:02 a.m., some three hours after arriving, police used explosives to breach the building. That's when Mateen was killed in a shootout with police.

Mina's presentation notes that officers rescued people throughout the night.

He said he doesn't know if any victims were struck by police gunfire.

The Orlando Police Department was one of 27 agencies responding to the shooting, which also wounded 68 people.

The presentation includes self-assessments and ways the agency might approach such situations differently in the future. It notes better coordination with local fire departments could lead to better communication. Mina said the Orlando Fire Department and Orange County Fire Rescue were not in his agency's command post outside the club.

The west bar in the Pulse Nightclub, where Omar Mateen killed 49 people, in Orlando, Florida, U.S. is pictured in this image released as part of a briefing document by the Orlando Police on April 13, 2017

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The south bathroom in the Pulse Nightclub, where Omar Mateen killed 49 people, in Orlando, Florida, U.S. is pictured in this image released as part of a briefing document by the Orlando Police on April 13, 2017

The exterior of the north bathroom of the Pulse Nightclub, where Omar Mateen killed 49 people, in Orlando, Florida, U.S. is pictured in this image released as part of a briefing document by the Orlando Police on April 13, 2017

One of the restrooms is seen after police punched a hole in the wall to get into the club

The southeast bathroom, where about four people hid during the standoff, is pictured above

One of the officers was shot in the head, but was saved by a kevlar helmet he was wearing (above)

'Would that have saved any more lives? No. The people who needed care, got care,' Mina said. 'But the communication would have been better between our two agencies if someone from the fire department would have been in our command post.'

The presentation says that fire department officials said the 'indirect communication' with law enforcement prevented crews from being informed of the wall breach. For example, many firefighters didn't know police would use explosives to breach the nightclub.

Police included this layout of the club in their report

Another 20 victims died on the dance floor, without even time to react, the report reveals